[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 011757
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT MON SEP 01 2008

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF
SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM THE
EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON SATELLITE
IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER OBSERVATIONS...AND
RADAR.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURES...

THE CENTER OF GUSTAV MADE LANDFALL ALONG THE LOUISIANA COAST NEAR
COCODRIE ABOUT 1430 UTC AS A CATEGORY TWO HURRICANE ON THE
SAFFIR-SIMPSON SCALE. AT 01/1800 UTC...ITS CENTER IS NEAR 29.7N
91.3W OR ABOUT 50 NM SE OF SOUTHEAST OF LAFAYETTE LOUISIANA AND
NEAR MORGAN CITY LOUISIANA MOVING NW AT 13 KT. THIS GENERAL
MOTION IS EXPECTED TO CONTINUE WITH A DECREASE IN THE FORWARD
SPEED DURING THE NEXT COUPLE OF DAYS. THE CENTER OF GUSTAV WILL
TRACK ALONG THE SOUTH CENTRAL LOUISIANA COAST THIS
AFTERNOON...THEN MOVE INTO WESTERN LOUISIANA TONIGHT AND EASTERN
TEXAS ON TUESDAY. THE MINIMUM CENTRAL PRESSURE JUST REPORTED BY
AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS 955 MB.
MAXIMUM SUSTAINED WIND SPEED IS 95 KT WITH GUSTS TO 115 KT. SEE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. AN EXTREMELY DANGEROUS
STORM SURGE OF 10 TO 14 FEET ABOVE NORMAL TIDAL LEVELS IS
EXPECTED NEAR AND TO THE EAST OF WHERE THE CENTER OF GUSTAV
CROSSES THE COAST. IN ADDITION...GUSTAV IS EXPECTED TO PRODUCE
TOTAL RAINFALL ACCUMULATIONS OF 6 TO 12 INCHES OVER PORTIONS OF
LOUISIANA...SOUTHERN AND WESTERN MISSISSIPPI...ARKANSAS AND
NORTHEASTERN TEXAS...WITH ISOLATED MAXIMUM AMOUNTS OF UP TO 20
INCHES POSSIBLE THROUGH THURSDAY. A FEW TORNADOES ARE ALSO
POSSIBLE OVER THE CENTRAL GULF COAST THIS AFTERNOON. DURING THE
LAST HOUR...THE NATIONAL OCEAN SERVICE AUTOMATED STATION AT
AMERADA PASS LOUISIANA REPORTED SUSTAINED WINDS OF 61 MPH...98
KM/HR...AND A WIND GUST OF 82 MPH...132 KM/HR.

AT 1730 UTC...HANNA BECOMES THE FOURTH HURRICANE OF THE SEASON.
AT THIS TIME...ITS CENTER IS NEAR 22.4N 72.6W OR VERY NEAR
MAYAGUANA ISLAND IN THE SE BAHAMAS MOVING W-SW AT 2 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 985 MB. MAXIMUM SUSTAINED
WIND SPEED IS 65 KT WITH GUSTS TO 80 KT. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC
FOR MORE DETAILS. A SLOW MOTION TOWARD THE WEST-SOUTHWEST OR
SOUTHWEST IS EXPECTED TODAY FOLLOWED BY A TURN TOWARD THE WEST
AND NORTHWEST ON TUESDAY. HANNA WILL BE MOVING OVER THE
SOUTHEASTERN AND CENTRAL BAHAMAS DURING THE NEXT COUPLE OF DAYS
PRODUCING RAINFALL AMOUNTS OF 4 TO 8 INCHES... WITH ISOLATED
MAXIMUM AMOUNTS OF UP TO 12 INCHES POSSIBLE THROUGH THURSDAY.
WATER VAPOR IMAGERY SUGGESTS THAT THE UPPER-LEVEL LOW WHICH HAD
PREVIOUSLY INHIBITED DEVELOPMENT HAS DISSIPATED...ALLOWING HANNA
TO RAPIDLY REACH HURRICANE STATUS. NUMEROUS STRONG CONVECTION IS
FROM 21N-24N BETWEEN 71W-74W. PART OF THIS STRONG SHOWER/TSTM
ACTIVITY IS ALREADY AFFECTING THE SE BAHAMAS WITH SOME SHOWERS
REACHING EASTERN CUBA...THE WINDWARD PASSAGE AND HISPANIOLA.

SATELLITE IMAGES AND SURFACE DATA INDICATE THAT THE LOW PRESSURE
AREA ASSOCIATED WITH A TROPICAL WAVE THAT HAS BEEN TRACKED OVER
THE EASTERN TROPICAL ATLANTIC FOR THE PAST FEW DAYS HAS BECOME
BETTER ORGANIZED...AND HAS NAMED TROPICAL DEPRESSION NINE. AT
01/1500 ITS CENTER IS LOCATED NEAR 17.6N 39.5W OR ABOUT 1275 NM
EAST OF THE LEEWARD ISLANDS. SEE LATEST NHC FORECAST/ADVISORY
UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS.
THE DEPRESSION HAS DEVELOPED PLENTY OF CONVECTION...NUMEROUS
CYCLONICALLY CURVED BANDS AND A WELL ESTABLISHED OUTFLOW. IT
COULD BECOME A TROPICAL STORM LATER TODAY.. AND THE FORECAST IS
TO REACH HURRICANE STATUS OVER THE NEXT SEVERAL DAYS AS IT MOVES
OVER THE WARM OCEAN IN A LOW SHEAR ENVIRONMENT. A STRONG
SUBTROPICAL RIDGE THAT IS FORECAST BY THE COMPUTER MODELS TO
EXPAND WWD WILL STEER THIS TROPICAL CYCLONE IN A GENERAL WEST TO
W-NW TRACK FOR THE NEXT 2 TO 3 DAYS.

A STRONG TROPICAL WAVE HAS EMERGED OFF THE WEST COAST OF AFRICA
AND IS SEVERAL HUNDRED MILES SOUTHEAST OF THE CAPE VERDE
ISLANDS. A 1007 MB SFC LOW IS ALONG THE WAVE AXIS NEAR 12.5N
19.5W. THIS SYSTEM IS SHOWING SIGNS OF ORGANIZATION WITH MORE
BANDING FEATURE AND A CLUSTER OF MODERATE TO STRONG CONVECTION.
THIS SYSTEM HAS THE POTENTIAL TO BECOME A TROPICAL DEPRESSION
LATER TODAY OR TOMORROW AS IT MOVES WESTWARD AT 15 TO 20 MPH.

...TROPICAL WAVES...
THE TROPICAL WAVE THAT WAS ALONG 52W ON THE 0600 UTC SFC MAP
HAS SHEARED. THE NORTHERN PORTION IS PRODUCING A LARGE AREA OF
CLOUDINESS AND THUNDERSTORMS FROM 25N-31W BETWEEN 48W-52W.
DEVELOPMENT OF THIS SYSTEM...IF ANY...WILL BE SLOW TO OCCUR AS
IT MOVES TOWARD THE NORTHWEST AT 10 TO 15 MPH. THE SOUTHERN
PORTION OF THE WAVE IS MOVING WWD. ITS AXIS IS NOW ALONG 57W
SOUTH OF 20N. A 1008 MB LOW IS ALONG THE WAVE AXIS NEAR 17N.
THIS SYSTEM IS PRODUCING DISORGANIZED SHOWERS AND THUNDERSTORMS.
ALTHOUGH SURFACE PRESSURES ARE LOW IN THE AREA...UPPER-LEVEL
WINDS ARE NOT FAVORABLE FOR SIGNIFICANT DEVELOPMENT OF THIS
SYSTEM AS CONTINUES TO MOVES SLOWLY WESTWARD APPROACHING THE
LESSER ANTILLES. A SFC TROUGH IS ANALYZED BETWEEN THESE TWO
AREAS OF CONVECTION AND LIES ALONG 51W FROM 20N-28N. AN EARLIER
QSCAT PASS SHOWED CLEARLY THE WIND SHIFT ASSOCIATED WITH THIS
TROUGH.

...THE ITCZ...

THE ITCZ AXIS IS ANALYZED ALONG 11N15W 11N25W 12N35W 11N44W
12N51W 11N60W. BESIDES THE CONVECTION MENTIONED IN THE SPECIAL
FEATURES AND TROPICAL WAVE SECTIONS...THERE IS A CLUSTER OF
MODERATE CONVECTION FROM 12N-15N BETWEEN 28W-32W. ISOLATED
MODERATE CONVECTION IS NEAR 12N34W AND 11N38W.

...DISCUSSION...

GULF OF MEXICO...
THE SURFACE MAP TODAY IS A TYPICAL ONE OF THE MONTH OF SEPTEMBER
WITH SEVERAL TROPICAL CYCLONES/LOWS. THE MOST IMPORTANT IS
HURRICANE GUSTAV...CURRENTLY MOVING OVER SE LOUISIANA...
FOLLOWED BY T.S. HANNA AND THE NEW T.D. NINE. WE ARE KEEPING AN
EYE ALSO IN AN AREA OF DISTURBED WEATHER LOCATED EAST OF THE
LEEWARD ISLANDS AND A STRONG TROPICAL WAVE THAT HAS EMERGED OFF
THE WEST COAST OF AFRICA. SEE SPECIAL FEATURES ABOVE FOR
DETAILS. DOPPLER RADAR SHOWS THE WELL DEFINED CIRCULATION OF
HURRICANE GUSTAV OVER SE LOUISIANA. AT 1600 UTC...IT WAS NEAR
MORGAN CITY LOUISIANA. LOW SURFACE PRESSURES...AT OR BELLOW 1012
MB CONTINUES TO COVER THE ENTIRE GULF DUE TO THE PRESENCE OF
HURRICANE GUSTAV. OUTER RAINBANDS FROM GUSTAV AR AFFECTING THE
N-CENTRAL GULF. A LINE OF SHOWERS WITH ISOLATED TSTMS EMBEDDED
IN THE CIRCULATION OF GUSTAV HAS FORMED OVER THE EASTERN GULF
AND EXTENDS FAR SOUTH TO THE FLORIDA KEYS. ALOFT...UPPER LEVEL
ANTICYCLONE CENTER OVER THE SE GULF DOMINATES THE AREA INCLUDING
ALSO THE SE CONUS AND THE STATE OF FLORIDA.

CARIBBEAN SEA...
SW 20-25 KT WINDS ARE AFFECTING THE WINDWARD PASSAGE ASSOCIATED
WITH THE CIRCULATION OF HANNA. OTHERWISE...TRADES ARE EXPECTED
TO BE LIGHT TO MODERATE THROUGH THE PERIOD AS THE ATLC RIDGE
REMAINS GREATLY WEAKENED DUE TO PRESENCE OF HANNA N OF AREA.
IN THE UPPER LEVELS...MOSTLY EASTERLY FLOW IS NOTED OVER THE
CARIBBEAN. HIGH CLOUDS ASSOCIATED WITH THE OUTFLOW OF HANNA ARE
SPREADING OVER PUERTO RICO AND HISPANIOLA AS WELL AS OVER THE
CENTRAL CARIBBEAN. SUBSIDENCE AND DRY AIR IS SEEN SOUTH OF 15N
AND E OF 75W TO THE WINDWARD ISLANDS. SOME CONVECTIVE ACTIVITY
IS OVER THE SW CARIBBEAN VERY CLOSE TO THE COLOMBIAN COAST.

ATLANTIC OCEAN...
A 1026 MB HIGH IS SW OF THE AZORES NEAR 34N30W EXTENDING A RIDGE
OVER PARTS OF THE CENTRAL AND EASTERN ATLC. THERE ARE SEVERAL
TROPICAL SYSTEMS ACROSS THE FORECAST AREA. SEE ABOVE. IN THE
UPPER LEVELS...AN INVERTED TROUGH EXTENDS SOUTH INTO THE
TROPICAL ATLC ALONG 52W/53W. AN UPPER LEVEL HIGH IS CENTERED
NEAR 29N39W WHILE AN UPPER-LEVEL TROUGH EXTENDS FROM AN
UPPER-LEVEL LOW NEAR 30N18W TO 23N30W.

$$
GR





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